Inhibition of the SOD activity in tumour-bearing animals treated with ATN-224 for 10 days was 65–80% at a concentration that is approximately two- to three-fold higher than the concentrations reported for antitumour activity in mice, suggesting that ATN-224 may not be exerting a significant direct effect in tumour cells, at least in a xenograft model. This evidence concerns the gene SOD1 and neoplasm.